Ross’ 1975 CB750

[Galactica]

Oh man. Don’t ask me to repeat the effort.  Not happy with it anyway. 

[Twisted_Twin]

Looking great Ross! Well done!

[Galactica]

So, yesterday I took the CB750 out for its first real shakedown ride.  Roy and I rode out to Agassiz.  There was a fellow out there who was selling a Dyna electronic ignition for $35.  I reckoned if it’s in working order, that’s a pretty good deal.  In any case it was a good reason to get my ass out for a ride. 

We headed out on the freeway.  I wanted to run it at speed and temperature to burn off the moisture that has been in the crankcase since I started it.  The bike ran well, as I expected.  An issue that’s become very apparent is the amount of effort it takes to turn the throttle.  It was an inordinate amount.  I’d only run it about 100 miles around town at this point.  I put it down to an overly strong carb return spring.  But as our ride progressed, the wrist twisting effort became greater, and the throttle seemed to catch and bind upon input.  Hmmm.

So this evening I pulled the tank and disconnected the throttle cables.  The return spring seemed absolutely fine when actuated be hand.  Hmmm.  The pull cable seemed a bit catchy though.  I opened up the right hand switch block to access the throttle grip tube.  Disconnected and inspected the cables there.  Really odd.  On the pull cable, the inner sheath had been pulled up and was wrapping along with the cable around the throttle tube.  Apparently, somehow the sheath has been pulled from inside the cable housing.  I pushed the inner sheath back down out of the way and applied some 3in1 oil.  Reconnected the cables to the carbs.  Feels great.  Now, if the issue reoccurs, I’ll have to replace the cable.  Cheap Chinese sh*t. 

Another small issue I noticed was a catch when I applied the rear foot brake.  I found that I had the upper bolt of the brake torque arm installed the wrong way.  The threaded end was catching on the actuator rod.  I removed the bolt, flipped it around so the threaded end was the other way.  Clearance achieved. 

These operations were performed under the influence of wine with dinner and bourbon afterwards.  So I’ll not be testing my repairs this evening.  That’ll wait until the ride to coffee at the Fort tomorrow.

[Hawkeye]

Ross, when I put a Dyna on my '77 CB750 some years ago, it was $180. I'd say you did well.

[Steve G.]

  50 year old cables tend to act like 50 year old cables.

[Galactica]

  50 year old cables tend to act like 50 year old cables.

These are new aftermarket cables.

[Twisted_Twin]

My LeMans has a Dyna ignition, you'll love it.

Coils are a bit spendy if you need to replace them but well worth it in the long run.

Glad you're getting it sorted out.

[kilowop]

Glad you're making progress on the old girl. I have a habit of lubing the various cables each spring, prior to the first ride. Worked well, so far.  Over the years I've accumulated a box full of good used cables, throttle, choke, etc.  Even have a number of Hydraulic Brake lines I've rescued. If anyone needs something like that contact me with details.  It will only cost you the mailing fee.

[Galactica]

Ok.  So I’ve ridden the bike about 300 miles.  Today my grandson had a baseball game that I attended.  When I left my garage, cold engine, I noticed a slight shudder as I engaged the clutch.  Hmmm.  I stopped and started again. No issue, so I went to the game.  All seemed fine until I approached the parking lot.  Leaving a stop sign, a pretty significant shudder upon clutch engagement.  Damn.  On the way home it occurred again with an accompanying significant rattle, which could have been the engine complaining about it.  I’ve not felt this kind of shudder anytime in the past.

Should I just go ahead and replace the plates, discs, and springs?  Are the parts at Vintage CB750 good quality?  I guess I’ll need the special tool as well.

Please chime in.

Cheers

[Steve G.]

  Been a while since I replaced a wet multiplate clutch, a year ago. New gasket, 10mm socket, new friction plates and clutch discs, proper torque specs for the 7-9 bolts to torque it down. I’ve never replaced the springs.
 What viscosity of oil you running?

[Bucko]

In all the clutches I've ever replaced (or had out for other maintenance reasons) over the years, not once have I ever found a single metal clutch plate out of OEM spec.  I've replaced the clutch diaphragm spring on both my Vulcans (those springs are a known weak point that lead to clutch slipping).  In both cases, even the fibre plates measured well within spec.

[hardrockminer]

I've never had a fibre plate measure less than the spec.  And I've never had a steel plate appear warped.  But I've had a couple of cracked or broken fibre plates.  I've replaced the springs on several clutches but not the big springs on the inner hub.  I don't have the tools to change those.

[rz5mark]

Be sure the hub bearing or bushing is in good shape.

[Galactica]

Ya, I laid awake much of last night with it going through my mind.   I actually am fairly certain it’s not the clutch.  It reminds very much of the KZ1000 LTD I did.  The dogs and slots on a couple of transmission gears were worn and it jumped out of gear under load. 

I posted on the SOHC forum.  It was suggested that there’s an Allen screw on the end of the shift barrel that holds on the gear shift side plate that has possibly come loose.  Have to pull off the left side transmission cover to check.  Requires having a new gasket on hand.  I’ll order one today.  I’ll see if they’re available at Honda.  I’m sure hoping I don’t have to split the cases. 

[Galactica]

Left side transmission/shifter cover gasket ordered.  Hopefully it will be here end of next week.